1. Field of the Invention
The present invention relates to an armrest, which is placed at the front edge of the keyboard to help in using the keyboard and mouse by supporting the forearms (i.e., the arm area from approximately the elbow to approximately the wrist, not simply the wrist or palm). More specifically, the armrest supports most of the forearm, ranging from the elbow to the wrist, and allows the operator to handle the mouse with the forearm supported close to the keyboard.
2. Description of the Prior Art
The operation of keyboards is involved in a large portion of manual visual display terminal (VDT) operations such as data input, for example. These operations are responsible for a high incidence of health hazards such as neck, shoulder, and arm syndrome because of the motions involved in continually maintaining the forearms in a lifted position without any support and repetitively using the arms and fingers. The inventors of the instant application have also proposed an armrest for VDT operations (Japanese Registered Utility Model Gazette No. 2505528).
Recent dramatic innovations in operating systems have brought the graphical user interface (GUI) approach into the mainstream of man-machine interface technology and enabled mouse operation to be integrated with traditional keyboard operation in almost every computing setting.
It is known that the health hazards associated with VDT operation result from muscular or nervous fatigue induced by a specific working posture in which the neck is inclined forward and the arms are held, without any support, away from the trunk. Another factor contributing to this fatigue is the workload on the fingers in running the keyboard. Now that mouse operations have been added to traditional VDT operations, it is necessary to examine possible solutions for improving operability and mitigating fatigue.
So far, several resting devices for wrists and for palms (hereafter collectively referred to as "palmrests") have been suggested for reducing fatigue. These proposed devices have not adequately taken into account possible improvements in operability (and reduction of fatigue) focused on mouse operation.
The majority of the existing palmrests are configured with the mouse pad separate which is physically separate from the keyboard pad (a "separate-type" palmrest) while a few of the existing palmrests have been designed to combine the mouse pad with the keyboard pad (an "integrated-type" palmrest). As one example, Japanese Registered Utility Model Gazette No. 3043575 discloses a integrated-type palmrest which is placed on the top of a desk together with a board for the keyboard. The palmrest is configured with a mouse pad that can be drawn out from the board, to the right of the keyboard and at a lower level than the top surface of the palmrest.
The second prior art integrated-type palmrest is placed on the top of a desk together with a board for the keyboard. This palmrest is configured with the mouse pad attached to the board on the right of the keyboard and at a lower level than the top surface of the palmrest. The third integrated-type palmrest disclosed in Japanese Patent Gazette No. 2687814 is integrated with a keyboard arrangement board and a mouse operating board which is placed midway between the keyboard and the computer monitor or cathode-ray tube (CRT) at almost as high a level as the top surface of the palmrest.
In the case of a mouse pad placed to the right of the keyboard, it can be reasonably suggested that a significant distance (approx. 41 cm) between the thumb (on the space bar) and the mouse pad would degrade the operability when both are used concurrently. This is because the right hand is repeatedly moved over this distance, and there is a heavy load on the shoulder girdle muscle during internal rotation and external rotation of the right humeral articulation, and on the trapezius (shoulder) during the abduction of right humeral articulation. Internal rotation affects the infraspinatus and teres minor muscle, while external rotation affects the infrascapular muscle, teres major muscle, pectoralis major muscle and the latissimus dorsi muscle.
In another prior art model the mouse pad is placed behind the keyboard. This arrangement makes it necessary to handle the mouse with the elbow sustained away from the trunk. As a result, the trapezius and brachial muscles (deltoid muscle) suffer a significant muscular load during the operation. The substantial distance (approx. 28 cm) between the space bar and mouse pad imposes a great muscular load to the brachial muscle which is lifted up and down across the keyboard. There are also other potential problems during mouse operations including inadvertent keystrokes when reaching for the mouse.
It should be noted that the effectiveness of armrests in mouse and keyboard operations is undisputed as it has been reported that armrests reduce the electromyograms of the brachioradial muscle, the bicep brachii, the deltoid muscle, the infrascarpular muscle and the trapezius, as compared with those when it was not used. When a working environment involving keyboard and mouse operations and the resultant working posture is closely analyzed from the viewpoint of health hazard prevention, an armrest should feature the following configurations.
First, the armrest should be adequately wide to extensively support the overall forearms, ranging from the wrist through the elbow. The forearm support of the armrest should also protrude (widen) towards the operator around its ends in order to provide support for the forearms positioned at the sides of the operator. The height of the armrest should also be adjustable and should incline downward away from its center, interfacing the space bar toward the lateral ends and the operator. This design is necessary in order to minimize lifting of the shoulders and to obtain better contact between the forearm and the surface of the armrest. Furthermore, the armrest should provide an area for using the mouse which extends from about 5 cm to the left of the center to about 10 cm to the right of the number keypad. An enlarged support area should be supplied on the right side of the armrest to support the right forearm during mouse operations. Finally, the armrest should be securable to the front edge of the desk and capable of pivoting towards the keyboard using hinges attached at its longitudinal ends or distal bottom in order to be usable for some shallow desks.